GROWING TOOLS
USDA Hardiness Zone Finder (ZIP Code)
A USDA hardiness zone is the average annual extreme low, in 10°F zones and 5°F half-zones. The 2023 map uses 1991–2020 temperatures. Your ZIP’s zone says whether a perennial is likely to survive winter. It is not the last frost date. This tool returns the half-zone, the °F range, and a link to frost dates.
The 2023 USDA Plant Hardiness Zone Map, built by the PRISM Climate Group at Oregon State University from 1991–2020 annual extreme lows, assigns each listed ZIP a half-zone. Zone 7b means an average annual extreme low of 5 to 10°F. Zone 6a means −10 to −5°F. Zone 5a means −20 to −15°F. Half-zones step by 5°F from zone 1a through 13b. On this page, ZIP 10001 is zone 7b, so the extreme-low range to quote is 5 to 10°F. ZIP 55450, near the Minneapolis station, is zone 5a. ZIP 33152, near Miami, is zone 11a, which is 40 to 45°F. A zone answers whether a perennial or bulb is likely to live through winter. It does not answer the last spring frost. Two ZIPs in one metro can differ by a half-zone, which is why this tool uses the ZIP list instead of a statewide label. This page is not the official USDA map. Confirm a borderline garden at planthardiness.ars.usda.gov, then use the frost-date tool for the planting calendar.
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Example hardiness zone
ZIP 10001 is USDA zone 7b on the 2023 map. The average annual extreme low is 5 to 10°F. A zone answers winter survival. Open frost dates for the planting calendar.
Which temperature is a zone?
| Zone | Extreme low |
|---|---|
| 1a | -60 to -55°F |
| 1b | -55 to -50°F |
| 2a | -50 to -45°F |
| 2b | -45 to -40°F |
| 3a | -40 to -35°F |
| 3b | -35 to -30°F |
| 4a | -30 to -25°F |
| 4b | -25 to -20°F |
| 5a | -20 to -15°F |
| 5b | -15 to -10°F |
| 6a | -10 to -5°F |
| 6b | -5 to 0°F |
| 7a | 0 to 5°F |
| 7b | 5 to 10°F |
| 8a | 10 to 15°F |
| 8b | 15 to 20°F |
| 9a | 20 to 25°F |
| 9b | 25 to 30°F |
| 10a | 30 to 35°F |
| 10b | 35 to 40°F |
| 11a | 40 to 45°F |
| 11b | 45 to 50°F |
| 12a | 50 to 55°F |
| 12b | 55 to 60°F |
| 13a | 60 to 65°F |
| 13b | 65 to 70°F |
Downtown Chicago ZIP 60601 is zone 6b (-5 to 0°F). The ZIP nearest Chicago’s airport station, 60106, is zone 6a (-10 to -5°F). Use the ZIP you garden in. Then read flowers to plant each season, flowers to plant in fall, spring bulbs, or tomatoes.
Common questions
Is a USDA zone the same as a frost date?+
No. The zone is the average annual extreme low temperature. Frost dates are calendar days. A zone 7b garden and a zone 7b garden in another region can have different last-frost dates. Use the frost-date tool for the calendar.
What does the “a” or “b” half-zone mean?+
Each numbered zone spans 10°F. The “a” half is the colder 5°F and the “b” half is the warmer 5°F. Zone 7a is 0 to 5°F. Zone 7b is 5 to 10°F.
Why is my ZIP different from the city I searched?+
The 2023 list is by ZIP, and a metro can cover more than one half-zone. Chicago ZIP 60601 and ZIP 60106 are not the same half-zone. Enter the ZIP you garden in.
What if my ZIP is missing?+
The 2023 ZIP list does not include every code. Use the official map at planthardiness.ars.usda.gov for a missing ZIP. Do not borrow a neighboring state’s single zone.
Sources and notes
ZIP zones are the 2023 PRISM listings, used unaltered. This page is not the official USDA map. Sources checked November 4, 2026. Editorial responsibility.